Rotary mechanical end face seals having two adjacent relatively rotating rings have been used to seal fluids of many types, including gases, some of which are toxic or environmentally harmful, and liquids, such as highly volatile light hydrocarbon liquids. Some of these seals use specific configurations of the seal elements which include at least one ring having an end face with a plurality of spiral grooves for pumping fluid into a gap which arises between the end faces of the ring during seal operation. The spiral grooves extend at least partially into an area where the two rings are confronting each other, thereby defining an interface area.
Configurations are known in which seal systems have dual seal modules for sealing around the shaft. These configurations include a number of different arrangements in which the seal modules are in a dual or tandem configuration. Examples of dual sealing modules in a seal system can be found in U.S. Pat. No. 4,290,611, which is assigned to the assignee of the present invention.
In certain sealing system applications, the ambient environment is not necessarily atmosphere, but may comprise a fluid or even a liquid. For example, in some dual seal module arrangements, the shaft is mounted on an oil bearing, which includes oil as the fluid environment in the space immediately downstream of the second or outboard module. The oil in a seal having an outer diameter (O.D.) pressurized configuration with grooves extending from the O.D. tends to seep along the shaft and into the gap formed between the seal rings. As the oil meets the rotating ring, there is a tendency for the oil to cling to the ring material and to be propelled by the centrifugal force of the rotating ring. The oil then enters into the seal gap, thereby fouling the seal and causing imbalance in the components of the seal.
The possibility of disposing the grooves and pressurization along the inner diameter of the sealing faces has been suggested. However, it has been found that inner diameter (I.D.) pressure of a process fluid at a level slightly above atmospheric can cause a conventional carbon graphite primary ring to succumb to the excess pressure and to cause the ring to fracture and eventually come apart. Whereas the external pressure of an O.D. pressurized sealing module causes compressive forces which aid in maintaining the ring integrity, the I.D. pressurization operates in the opposite direction. Unless the I.D. pressurized ring includes some means to maintain its structural integrity, I.D. pressurization cannot provide a solution to the oil contamination problem.
What is thus needed is a seal configuration which avoids the problems caused by oil contamination in the seal by utilizing the centrifugal force of the rotating ring to impede the entry of oil into the seal gap rather than to aid such entry.
A further need arises for a ring for use in a rotary mechanical end face seal that is able to maintain its integrity and to continue operating under conditions of I.D. pressurized process fluid.